It is common practice in the medical field for a physician to insert a cannula through a natural opening in the patient's body, such as the nasal or oral openings, or through an incised opening, and to advance the cannula to a particular location within the body. For example, such a cannula may take the form of an endotracheal tube. The distal end of the tube is typically inserted through the oral or nasal openings of the patient, advanced past the larynx and pharynx and positioned in the trachea. The proximal end of the endotracheal tube remains outside of the patient's body and can be attached to respiratory equipment, in order to assist the patient's breathing, or to anesthetic equipment so that anesthetic gas can be administered to the patient prior to surgery.
Another example of cannulas placed within the body is a tracheostomy tube, such as that described and claimed in the U. S. Pat. No. 3,693,624, assigned to Shiley, Inc., assignee of the present invention. Such tracheostomy tubes are generally inserted into the trachea of the patient through an incision in the neck. Other cannulas in common used today include catheters, which are inserted into ducts or vessels within the patient's body. Specifically, a cardiac catheter may be inserted into a blood vessel and abrasively passed along the interior walls of the vessel in order to remove fatty cholesterol accumulation thereon.
In order to properly place these cannulas, and especially their distal tips, within the body so that they will accomplish their intended purpose without injuring the patient's internal tissue, a physician or radiologist typically utilizes an X ray photograph or a fluoroscope to examine the location of the cannula within the body. In fact, it is common in the internal placement of some cannulas, e.g. endotracheal tubes, to utilize a fluoroscope to visually monitor the location of the cannula as it is inserted and placed within the body. Therefore, it is necessary that the cannula (or some portion of it) be radiopaque.
Certain prior cannulas, however, were constructed so as to be entirely radiopaque. Thus, placement of the cannula by the physician or radiologist was hindered since the radiopaqueness of the cannula obscured visual inspection of the cannula's position with respect to surrounding organs and tissue. Furthermore, such completely radiopaque cannulas precluded the use of a clear material in constructing the cannula, thereby disadvantageously preventing the use of a common diagnostic technique involving the visual examination of fluids or other matter that may accumulate within the proximal, external portion of the cannula.
Other cannulas presently in use are completely clear, except for their distal ends which are provided with a radiopaque marker to indicate the location of the cannula without obscuring the view of surrounding body parts. To provide such markers, thin strips or rings made of radiopaque materials, such as metal, are embedded in the cannula near its tip. Such radiopaque inserts, however, resemble many similarly shaped body parts, and are therefore difficult to distinguish from such parts in an X ray or fluoroscopic image. Thus, the location of the cannula within the body is very difficult to determine, posing a risk of injury to the patient.
Even if the inserts are identified apart from surrounding body parts, the orientation of such small geographic shapes can be confusing, preventing the physician or radiologist from precisely locating the cannula tip. Furthermore, it is possible for such inserts, not being integral parts of the cannula, to become separated from the cannula and cause injury to the patient. Still other cannulas in common use have a radiopaque tip bonded to the distal end of the cannula by means of a solvent or adhesive. Again, however, since the cannula is not a unitary device, detachment of the tip within the patient's body poses a serious threat to the health and safety of the patient.